1. Field
A scroll compressor is disclosed herein.
2. Background
A scroll compressor refers to a compressor that utilizes a first or orbital scroll having a spiral wrap, and a second or non-orbital scroll having a spiral wrap, the first scroll performing an orbital motion with respect to the second scroll. While the first scroll and the second scroll are engaged with each other in operation, a capacity of a pressure chamber formed therebetween may be reduced as the first scroll performs the orbital motion. Hence, a pressure of a fluid in the pressure chamber may be increased, and the fluid discharged from a discharge opening formed at a central portion of the second scroll.
The scroll compressor performs a suction process, a compression process, and a discharge process consecutively while the first scroll performs the orbital motion. Because of operational characteristics, the scroll compressor may not require a discharge valve and a suction valve in principle, and its structure may be simple with a small number of components, thus making it possible to perform a high speed rotation. Further, as a change in torque required for compression is small, and the suction and compression processes consecutively performed, the scroll compressor is known to create minimal noise and vibration.
For the scroll compressor, an occurrence of leakage of a refrigerant between the first scroll and the second scroll should be avoided or kept at a minimum, and lubricity (lubrication characteristic) should be enhanced therebetween. In order to prevent a compressed refrigerant from leaking between the first scroll and the second scroll, an end of a wrap portion or wrap should be adhered to a surface of a plate portion or plate. On the other hand, in order for the first scroll to smoothly perform an orbital motion with respect to the second scroll, resistance due to friction should be minimized. The relationship between prevention of refrigerant leakage and enhancement of lubricity is contradictory. That is, if the end of the wrap portion and the surface of the plate portion are adhered to each other with an excessive force, leakage may be prevented. However, in such a case, more friction between the parts or components may result, thereby increasing noise and abrasion. On the other hand, if the end of the wrap portion and the surface of the plate portion are adhered to each other with less than an adequate sealing force, the friction may be reduced, but a lowering of the sealing force may result in an increase in leakage.
In order to solve such problems, a back pressure chamber having an intermediate pressure between a discharge pressure and a suction pressure may be formed on or at a rear surface of the first scroll or the second scroll. That is, the first scroll and the second scroll may be adhered to each other with a proper force, by forming a back pressure chamber that communicates with a compression chamber having an intermediate pressure, among a plurality of compression chambers formed between the first scroll and the second scroll. With such a configuration, leakage of refrigerant may be prevented and lubricity enhanced.
The back pressure chamber may be positioned on a lower surface of the first scroll or an upper surface of the second scroll. In this case, the scroll compressor with such a back pressure chamber may be referred to as a ‘lower back pressure type scroll compressor’ or an ‘upper back pressure type scroll compressor’ for convenience. The structure of the lower back pressure type scroll compressor is simple, and bypass holes easily formed. However, as its back pressure chamber is positioned on the lower surface of the first scroll, a form and position of the back pressure chamber may change due to the orbital motion. This may cause the first scroll to tilt, resulting in the occurrence of vibration and noise. Further, an O-ring to prevent leakage of compressed refrigerant may be rapidly abraded. The structure of the upper back pressure type scroll compressor is complicated. However, as the back pressure chamber of the upper back pressure type scroll compressor is fixed in form and position, the probability of the second scroll tilting is low, and sealing for the back pressure chamber is excellent.
Korean Patent Application No. 10-2000-0037517, entitled “Method for Processing Bearing Housing And Scroll Machine having Bearing Housing,” which corresponds to U.S. Pat. No. 5,156,539 and U.S. Reissue Pat. No. 35,216, all of which are hereby incorporated by reference, discloses an example of such an upper back pressure type scroll compressor. FIG. 1 is a partial cross-sectional view showing an example of an upper back pressure type scroll compressor. The scroll compressor 1 of FIG. 1 may include a first or orbital scroll 30 configured to perform an orbital motion on a main frame 20 fixedly-installed in a casing 10, and a second or non-orbital scroll 40 engaged with the first scroll 30 to create a plurality of compression chambers upon the orbital motion. A back pressure chamber (BP) may be formed at an upper portion of the second scroll 40, and a floating plate 60 to seal the back pressure chamber (BP) may be installed so as to be slidable up and down along an outer circumferential surface of a discharge passage 45. A discharge cover 22 may be installed at an upper surface of the floating plate 60, thereby dividing an inner space of the scroll compressor 1 into a suction space (S) and a discharge space (D). A lip seal (not shown) may be installed between the floating plate 60 and the back pressure chamber (BP), so that refrigerant may be prevented from leaking from the back pressure chamber (BP).
The back pressure chamber (BP) may communicate with one of the plurality of compression chambers, and may be at a receiving end of an intermediate pressure from the plurality of compression chambers. With such a configuration, pressure may be applied upward to the floating plate 60, and pressure may also be applied downward to the second scroll 40. If the floating plate 60 moves upward due to the pressure of the back pressure chamber (BP), the discharge space (D) may be sealed as an end of the floating plate 60 contacts the discharge cover 22. In this case, the second scroll 40 may move downward to be adhered to the first scroll 30. With such a configuration, a gap between the second scroll 40 and the first scroll 30 may be effectively sealed.
However, in the case of the above upper back pressure type scroll compressor, as an upper surface of the non-orbital scroll 40 is blocked by the back pressure chamber, bypass holes cannot be formed. To solve such a problem, Korean Patent Application No. 10-2012-7023733, entitled “Compressor having valve assembly”, discloses an example of such an upper back pressure type scroll compressor. As shown in FIG. 2, a hub member 76 is positioned at a central portion of back pressure chamber (BP), and is penetratingly-formed at the back pressure chamber (BP) in upper and lower directions. A valve assembly 28 is provided below the hub member 76. As the valve assembly is moved in the up/down direction in the hub member 76, bypass holes 90 and 92 formed on an upper surface of the non-orbital scroll are open and closed.
In the conventional art, an upper back pressure type scroll compressor is provided with the bypass holes to prevent an overload. However, due to the hub member arranged in the back pressure chamber, a position of the bypass holes cannot be arbitrarily set. That is, as the back pressure chamber must be arranged at a predetermined position with a predetermined size in order to obtain a sufficient back pressure, a size of the hub member is restricted. Thus, a position of the bypass holes is also restricted due to a load of the hub member.
Further, a floating plate should seal the back pressure chamber by contacting an inner surface of the back pressure chamber of the non-orbital scroll, and an outer circumferential surface of the hub member. In this case, a sealing function of the floating plate may be lowered due to a machining tolerance and a coupling tolerance of the hub member.
Further, as the floating plate and the hub member are separated from each other, a machining tolerance and an assembly tolerance occur. This may cause a difficulty in sealing a gap between the back pressure chamber and a discharge opening, and may increase production costs due to an increased number of assembly processes.